Most vehicle seats comprise a rigid frame assembly that includes a seat cushion section and a seat back section. Frequently, the seat cushion section supports a seat cushion formed of cushioning foamed material. A cover assembly is provided that includes a seat cushion panel that engages the foamed material of the seat cushion and a skirt extending from the periphery of the cover panel so as to cover the frame. For a seat back, the foam material is positioned on the front side of the frame and the cover assembly is formed as a bag that includes a front panel having an interior surface that engages the forward surface of the foam material and an exterior surface which is engaged by the back of the occupant when seated in the vehicle. A rear panel usually is provided that extends around and over the back of the frame.
The cushioning foam material within the cover assembly may be foamed in place. The cover is retained in its final desired contoured shape in the interior space within a mold. A shot of liquid foam-forming ingredients is injected into the cover while in the mold. The foam is allowed to cure while held in the mold so as to adopt the shape of the mold interior. Once the foam is cured, the final seating component or seat cushion assembly is removed from the mold.
If a vacuum mold is used, vacuum molding of the cover panel for seating components requires that the cover be made of a material that includes an impermeable layer. Most commonly, a thin layer of foam is laminated to the back surface of the fabric cover panel. In turn, an imperforate layer, such as a 2 mil thick layer of polyurethane film, is bonded or adhered to the thin foam layer. Thus, the thin foam layer is sandwiched between the rear surface of the fabric cover panel and the thin imperforate film layer.
The cover panel that is to receive the liquid foam-forming material during the foam in place molding most often is sewn together to create the seating component shape. The sewing frequently is performed at a different location from the molding operation. When sewing, it is possible for the imperforate film to be punctured. The film may also be weakened or punctured during transport. Any holes or cracks in the imperforate film allow liquid foam forming material to penetrate or seep through the imperforate film and contact the cover panel. Upon curing, the material forms hard spots in the cover. Hard spots are considered defects that may cause the cover panel to be rejected. In severe cases, foam even may strike through to the outer surface of the fabric, thus causing an unacceptable visual appearance.
Applying the imperforate film to the foam-cover panel laminate represents a further manufacturing step—adding time and expense to the seating component manufacture. In addition, the sewn seams of the cover panel necessarily puncture the imperforate film and may need to be covered with a tape or film, which is yet another processing step.
As one suggested solution, U.S. Pat. No. 5,468,434 proposes sewing the thin foam layer-fabric cover panel into the form of the desired seating component, then placing the imperforate film adjacent to the foam layer just before closing the mold for the foam in place operation, and heating the film to cure and bond it to the foam layer. Thereafter, the liquid foam forming material is introduced into the mold.
As another proposal, U.S. Pat. No. 4,959,184 suggests that penetration through the fabric panel can be prevented by predetermined careful control of the pressure within the mold cavity during the foam in place operation.
The industry thus continues to seek an economical solution to the bleed through/strike through problems encountered with foam in place seating component molding.